This invention relates to a paper tube used as a paper core for a roll of a photosensitive material, its production, and a package of a roll of a photosensitive material using it.
Photographic properties photosensitive materials, such as photographic films, are degraded if the materials are stored by under high humidity conditions (relative humidity: more than 80 %). Accordingly, in the case of paper tubes for photosensitive materials using an aqueous adhesive, it was necessary to dry the paper tube after winding the paper tape. In order to omit the drying process, it was necessary to apply a high concentration adhesive in a thin thickness, as well as to decrease moisture content of the paper tape. However, since the paper tape becomes fragile by decreasing the moisture content, a moisture content of more than 5% is necessary in the paper tape for putting it to practical use as the paper core. Moreover, when the concentration of adhesive is increased, providing a thin film coating of the adhesive is difficult due to a high viscosity. For example, a viscosity range suitable for providing a thin film coating, yet capable of providing a coating of adhesive with rare occurrences of streaks and unevenness by a roll coater is 1,000 to 10,000 (mPa.multidot.s) at 20.degree. C. by a Brookfield viscometer. When the concentration of an adhesive having a concentration of 45% and a viscosity of 6,000 is elevated to 50%, the viscosity becomes 30,000 which is outside the range, suitable for providing a thin film coating. The viscosity can be reduced by decreasing the viscosity of polyvinyl alcohol (PVA). However, when the viscosity of PVA was decreased, the initial adhesive force was decreased resulting in a loss of tube-forming ability. Thus, in the case of forming a paper core using an aqueous adhesive, it was difficult to omit the drying process.
As a method of omitting the drying process, Japanese Patent KOKOKU No. 58-48342 discloses a method of winding a film resin together with paper tape and adhering the paper tape by heating to melt the resin. The method requires heating at every winding which is troublesome in workability, and accordingly, the method is unsuitable for the production of multilayer paper, tubes as cores.